Method and apparatus for expedited domain name system query resolution

ABSTRACT

In one embodiment, a method and apparatus for resolving domain name system queries using unique top-level domains in a private network space are disclosed. For example, the method determines that a domain name service query specifies a destination residing in a private network space rather than in a public Internet space. The method then routes the domain name service query to a top-level domain name service server associated with the private network space, without routing the domain name service query to a root domain name service server in the public Internet space. The top-level domain name system server resides in the highest level of a hierarchy of domain name system servers belonging to the private network space.

This application is a continuation of U.S. patent application Ser. No.15/936,248, filed Mar. 26, 2018, now U.S. Pat. No. 10,257,154, which isa continuation of U.S. patent application Ser. No. 14/881,559, filedOct. 13, 2015, now U.S. Pat. No. 9,930,004, all of which are hereinincorporated by reference in their entirety.

The present disclosure relates to a method and apparatus for resolvingdomain name system queries using unique top-level domains in a privatenetwork space.

BACKGROUND

An Internet Protocol (IP) address is a unique numerical string (e.g.,18.72.0.3) that is assigned to a device that participates in a computernetwork using IP for communication. Because IP addresses are typicallydifficult to remember, the device may also be assigned a moredescriptive host name (e.g., host.att.net) that is easier to remember.The host name includes a domain name (e.g., att.net) that identifies arealm of administrative authority to which the device belongs. Domainnames are organized into hierarchical subdomains of a nameless rootdomain. For example, the subdomains may include top-level domains (e.g.,.net, .com, .edu) as well as lower-level domains that may be reserved byend users who wish to connect local area networks (LANs) to the Internetor to make certain resources such as web sites accessible to the public.

SUMMARY OF THE DISCLOSURE

In one embodiment, a method and apparatus for resolving domain namesystem queries using unique top-level domains in a private network spaceare disclosed. For example, the method determines that a domain nameservice query specifies a destination residing in a private networkspace rather than in a public Internet space. The method then routes thedomain name service query to a top-level domain name service serverassociated with the private network space, without routing the domainname service query to a root domain name service server in the publicInternet space. The top-level domain name system server resides in thehighest level of a hierarchy of domain name system servers belonging tothe private network space.

BRIEF DESCRIPTION OF THE DRAWINGS

The teaching of the present disclosure can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a block diagram depicting one example of a communicationsnetwork;

FIG. 2 is a block diagram depicting a portion of the communicationsnetwork of FIG. 1 in greater detail;

FIG. 3 illustrates a flowchart of an example method of the presentdisclosure for resolving domain name system queries in an expeditedmanner in a private network space; and

FIG. 4 depicts a high-level block diagram of a computer suitable for usein performing the functions described herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION

When an end user submits a query containing a host name to anetwork-supported service (e.g., an IP multimedia service) the DomainName System (DNS) resolves the corresponding IP address via ahierarchical system of servers. The end user's computer (or a proxy)will first query a root DNS server for the address of the serverassociated with the top-level domain. Then, the computer queries thetop-level domain's DNS server for the address of the server associatedwith the next-level domain. This processes continue iteratively, workingfrom the top-level domain to the lowest-level domain, until the IPaddress corresponding to the host name is resolved and returned to theend user's computer.

The round trip time (RTT) for traditional DNS resolution, includingqueries to the root server, is typically approximately one second ormore, which may be unacceptably long for IP-rich service termination.For instance, many critical mobility services such as short messagingservice, Voice over Long Term Evolution (VoLTE) services, or videocalling, demand quick RTT (e.g., less than approximately one hundredmilliseconds) for call setup. Moreover, many top-level domains are inthe pubic Internet space, and therefore may not be subject to the sameservice level agreements (SLAs) as, for example, a multiprotocol labelswitching (MPLS)-based virtual private network (VPN).

The present disclosure broadly describes a method, a computer-readablestorage device, and an apparatus for expedited domain name system queryresolution. Embodiments of the present disclosure implement a uniquetop-level domain within a private MPLS space that controls access tolower-level DNS servers and domains without requiring the routing ofqueries to a root DNS server. In addition, a DNS resolver is implementedthat is capable of determining when a DNS query specifies a destinationthat is in the public Internet space or in a private network space androuting the DNS query for resolution accordingly. The resolution speedmeets the requirements of services including mobility VoLTE, CarrierVoice over Internet Protocol (cVoIP), mobile switching centers (MSCs),Internet Imaging Protocol (IIP), Web Real-Time Communication (WebRTC),and IP-based interoperability. In addition to resolving queries morequickly, the present disclosure infrastructure is also capable ofexercising tighter control over access to DNS services, includingservices that are supported by a infrastructure residing in a privatenetwork space.

FIG. 1 is a block diagram depicting one example of a communicationsnetwork 100. In one example, the communications network 100 is anInternet Protocol (IP) network (e.g., an IP Multimedia Subsystem (IMS)network, a long term evolution (LTE) network, or the like). It should benoted that an IP network is broadly defined as a network that usesInternet Protocol to exchange data packets. Additional exemplary IPnetworks include Voice over IP (VoIP) networks, Service over IP (SoIP)networks, and the like.

In one embodiment, the network 100 may comprise a core network 102. Thecore network 102 may be in communication with one or more accessnetworks 120 and 122. The access networks 120 and 122 may include awireless access network (e.g., a WiFi network and the like), a cellularaccess network, a PSTN access network, a cable access network, a wiredaccess network and the like. In one embodiment, the access networks 120and 122 may all be different types of access networks, may all be thesame type of access network, or some access networks may be the sametype of access network and other may be different types of accessnetworks. The core network 102 and the access networks 120 and 122 maybe operated by different service providers, the same service provider ora combination thereof.

In one embodiment, the core network 102 may include a load balancer 104and a DNS resolver 106. Although only a single load balancer 104 and asingle DNS resolver 106 are illustrated, it should be noted that anynumber of load balancers 104 or DNS resolvers 106 may be deployed. Inone embodiment, the load balancer 104 and/or the DNS resolver 106 maycomprise a dedicated computer or application server as illustrated inFIG. 4 and discussed below.

In one embodiment, the load balancer 104 receives DNS queries directlyfrom network elements and selects DNS resolvers such as the DNS resolver106 to resolve the DNS queries. To this end, the load balancer 104 maymonitor the DNS resolvers, including the DNS resolver 106, in order todetermine their latency and workloads.

In one embodiment, the DNS resolver 106 may perform the methods andalgorithms discussed below related to resolving domain name systemqueries in an expedited manner in a private network space. Among otherfunctions, the DNS resolver 106 may route DNS queries to a hierarchy ofDNS servers in order to determine the IP address corresponding to a hostname specified in a DNS query.

In one embodiment, the core network 102 may further include thehierarchy of DNS servers, including DNS servers 116, 118, and 120. Atleast one of the DNS servers 116, 118, and 120 may be a privatetop-level DNS server that is not accessible within the public Internetspace.

In one embodiment, the access network 120 may be in communication withone or more user endpoint devices (also referred to as “endpointdevices” or “UE”) 108 and 110. In one embodiment, the access network 122may be in communication with one or more user endpoint devices 112 and114.

In one embodiment, the user endpoint devices 108, 110, 112 and 114 maybe any type of endpoint device such as a desktop computer or a mobileendpoint device such as a cellular telephone, a smart phone, a tabletcomputer, a laptop computer, a netbook, an ultrabook, a tablet computer,a portable media device (e.g., an MP3 player), a gaming console, aportable gaming device, and the like. It should be noted that althoughonly four user endpoint devices are illustrated in FIG. 1, any number ofuser endpoint devices may be deployed.

It should be noted that the network 100 has been simplified. Forexample, the network 100 may include other network elements (not shown)such as border elements, routers, switches, policy servers, securitydevices, a content distribution network (CDN) and the like.

FIG. 2 is a block diagram depicting a portion of the communicationsnetwork 100 of FIG. 1 in greater detail. In particular, FIG. 2illustrates some components of the core network 102 and the accessnetwork 120 (both access networks 120 and 122 may be configured asillustrated, but only access network 120 is shown for the sake ofsimplicity). The illustrated components are not meant to represent anexhaustive list of the components of each network, but rather representthe components necessary to support VoLTE service and other mobilityservices that may benefit from embodiments of the present disclosure.

Components of the access network 120 include an evolved Node B (eNodeB)200, a serving gateway (S-GW) 202, a PDN gateway (P-GW) 204, a mobilitymanagement entity (MME) 206, and a policy charging and rules function(PCRF) 208.

The eNodeB 200 interfaces with the user endpoint devices 108, 110 andperforms a plurality of functions including radio resource management,admission control, scheduling, enforcement of quality of service (QoS),cell information broadcast, ciphering and deciphering if user andcontrol plane data, and compression and decompression of user planepacket headers. To this end, the eNodeB 200 hosts a plurality of layers(i.e., physical, medium access control, radio link control, and packetdata convergence protocol) that include the functionality of user-planeheader-compression and encryption.

The S-GW 202 routes and forwards user data packets. In particular, allIP packets (signaling plus bearer) traverse the S-GW 202, which is thelocal mobility anchor for bearers when the user endpoint device 108 or110 moves between different eNodeBs or hands over to legacy 2G or 3Gnetwork access.

The P-GW 204 provides connectivity between the user endpoint devices108, 110 and external packet data networks. Specifically, the P-GW 204provides IP address management, QoS enforcement, and flow-based chargingaccording top policy rules received from the PCRF 208 in order to act asa mobility anchor for non 3GPP technologies (e.g., CDMA, WiMAX, WiFi,fixed broadband networks). The P-GW 204 also connects IP bearers to thepacket data networks.

The MME 206 is the control node for the LTE access network. The MME 206processes the signaling between the user endpoint devices 108, 110 andthe core network 102. To this end, the MME 206 performs bearermanagement (establishment, maintenance, and release) and connectionmanagement (establishing the data connection between the user endpointdevices 108, 110 and the core network 102).

The PCRF 208 provides policy control decisions and flow-based chargingcontrols. In particular, the PCRF 208 instructs the network aboutenforcement of QoS policies based on information received from asubscriber policy repository, which may be part of the core network 102(e.g., VoLTE or video bearer identifications).

Components of the core network 102 include a home subscriber server(HSS) 210, a proxy call session control function (P-CSCF) 212, aninterrogating/serving call session control function (I/S-CSCF) 214, anda multimedia telephony application server (MMTel AS) 216.

The HSS 210 is a database that contains user-related andsubscription-related data (e.g., QoS profiles, identification,authorization, and provisioned services). The HSS provides thisinformation to the MME during user authentication.

The P-CSCF 212 is the initial point of contact for session signaling forthe user endpoint devices 108, 110. In particular, the P-CSCF operatesas a session initiation protocol (SIP) proxy by forwarding SIP messagesbetween the user endpoint devices 108, 110 and the core network 102.

The I/S-CSCF 214 is the contact point within the core network 102 forall connections destined to a user of the core network 102. On IMSregistration, it interrogates the HSS 210 to determine to which servingcall session control function (S-CSCF) to route the request forregistration. For mobile terminating calls, the I/S-CSCF 214interrogates the HSS 210 to determine on which S-CSCF the user isregistered. The I/S-CSCF 214 provides session set-up, session tear-down,session control, and session routing functions. The I/S-CSCF 214generates records for billing purposes for all sessions under itscontrol and invokes applications using application servers. The I/S-CSCF214 also acts as a SIP registrar for user endpoint devices that the HSS210 and I/S-CSCF 214 assign to it. The I/S-CSCF 214 queries the HSS 210for the applicable user profiles and handles calls involving the userendpoint devices once the users have been registered. Depending on thefunction being performed, the description may make reference to theI/S-CSCF 214 as the “I/S-CSCF,” the “I-CSCF,” or the “S-CSCF.” Finally,the core network 102 may include the load balancer 104 and the DNSresolver 106 as discussed above.

The MMTel AS 216 is an IMS application server that provides support formultimedia telephony services as defined by 3GPP (e.g., supplementaryservice functionality).

FIG. 3 illustrates a flowchart of an example method 300 of the presentdisclosure for resolving domain name system queries in an expeditedmanner in a private network space, which in one embodiment is an IMSnetwork (which may support, for example, VoLTE and/or other services).In one embodiment, the method 300 may be implemented in a DNS resolver,e.g., the DNS resolver 106 of FIG. 1, or in the computer or processor asdescribed in FIG. 4.

The method 300 starts in step 302 and proceeds to step 304. In step 304,the DNS resolver receives a DNS query. The DNS query originates with anend-user device or a network element (e.g., a P-CSCF). The DNS query maybe routed to the DNS resolver via a load balancer that seeks to assignthe query to the DNS resolver having the lowest latency or lightestload. The DNS query may be sent in accordance with any cast addressingmethodologies that route queries to the topologically nearest node in agroup of potential receiving nodes. As an example, the DNS query mayoriginate with the P-CSCF 212 of FIG. 2 and may comprise the domain name“a.isc.ch1il.usp.att.net,” indicating that the P-CSCF element 212 istrying to reach the I-CSCF element 214.

In step 306, the DNS resolver determines whether the DNS query specifiesa destination within the public Internet space or within a privatenetwork space. If the DNS resolver concludes that the DNS queryspecifies a destination within the public Internet space, then, in step308, the DNS resolver routes the DNS query to a root DNS server so thatthe DNS query can be resolved in accordance with conventional DNSresolution protocols. The details of such protocols are known andtherefore not discussed in detail here. The method 300 ends in step 326after resolving the DNS query through conventional DNS protocols.

Alternatively, if the DNS resolver concludes that the DNS queryspecifies a destination in a private network space, then, in step 310,the DNS resolver bypasses the root DNS server and routes the DNS querydirectly to a private top-level DNS server. The private top-level DNSserver is part of a private network infrastructure, such as a privateMPLS space, and resides in the highest level within a hierarchy of DNSservers belonging to that private network infrastructure. For example,based on the example DNS query above, the domain name of the privatetop-level DNS server may be “usp.att.net.”

In step 312, the DNS resolver receives a response from the privatetop-level DNS server. The response includes the IP address for a secondDNS server—i.e., the second-level DNS server associated with the DNSquery. The second-level DNS server resides in a lower level of the DNSserver hierarchy relative to the top-level DNS server and may be asite-level private DNS server. For example, based on the example DNSquery above, the second-level domain server may be “ch1il.usp.att.net.”

In step 314, the DNS resolver routes the DNS query to the second-levelDNS server, using the IP address provided by the top-level DNS server.For example, based on the example DNS query above, the DNS query may berouted to “ch1il.usp.att.net.”

In step 316, the DNS resolver receives a response from the second-levelDNS server. The response includes the IP address for a third DNSserver—i.e., the next-(lower)-level DNS server associated with the DNSquery. The next-level DNS server resides in a lower level of the DNSserver hierarchy relative to the second-level DNS server. For example,based on the example DNS query above, the next-level domain server maybe “isc.ch1il.usp.att.net.”

In step 318, the DNS resolver routes the DNS query to thenext-(lower)-level DNS server, using the IP address provided by thesecond-level DNS server. For example, based on the example DNS queryabove, the DNS query may be routed to “isc.ch1il.usp.att.net.”

In step 320, the DNS resolver receives a response from the next-levelDNS server. The response may include the IP address for anext-(lower)-level DNS server associated with the DNS query, if there isone. Alternatively, the response may include the full IP address of theDNS fully qualified domain name (FQDN) corresponding to the domain namespecified in the DNS query (i.e., the resolution of the DNS query).

In step 322, the DNS resolver determines whether the response from thenext-level DNS server includes the IP address of a next-level DNS serveror a resolution of the DNS query. If the DNS resolver concludes in step322 that the response includes the IP address of a next-level DNSserver, then the method 300 returns to step 318 and routes the DNS queryto the next-level DNS server as discussed above.

Alternatively, if the DNS resolver concludes in step 322 that theresponse includes the resolution of the DNS query, then the method 300proceeds to step 324. In step 324, the DNS resolver routes the response(including the IP address corresponding to the domain name specified inthe DNS query) to the entity from which the DNS query originated. In oneembodiment, the response is routed via a load balancer. The originatingelement of the DNS query (e.g., the P-CSCF element in the example DNSquery above) may then use the IP address to connect to the appropriatenetwork element (e.g., the I-CSCF element in the example DNS queryabove).

The method 300 ends in step 326, after the DNS query has been resolved.

As such, the present disclosure provides expedited resolution of DNSqueries that are directed to destinations in a private network space,e.g., services that are provided over a private MPLS space. The DNSqueries can be resolved without routing the queries to a root DNSserver, thereby reducing the round trip time necessary to determine theroute.

Although the method 300 is described above within the example context ofrouting/call completion for IMS IP-based calls (e.g., as embodied by aP-CSCF element to I-CSCF element connection), the same principles can beused to facilitate other types of connections and services, includingcircuit-switched voice calling or mobility element (e.g., converged IPmessaging (CPM)) to universal service platform (USP) element (e.g.,S-CSCF) connections. In the latter case, the load balancer may beintegrated with the DNS resolver, and a mobility DNS server for themobility subdomain may be used to route queries and responses betweenthe mobility element and the DNS resolver/load balancer.

In addition to resolving queries more quickly, the disclosedinfrastructure is also capable of exercising tighter control over accessto DNS services. For instance, the method 300 may be used by a top-levelDNS server in a private network space to control which subdomains in theprivate network space can communicate with each other (e.g., whichsubdomains' DNS servers can communicate with each other). For instance,different services (e.g., mobility, WebRTC, IIP, etc.) may be associatedwith different dedicated DNS subdomains. This ability to tightly controlaccess to DNS services can facilitate memory caching on DNS resolvers,since there is less need to cache large domain tree structures.Maintaining only a small cache of MPLS records, for instance, allows DNSqueries to be resolved more quickly.

FIG. 4 depicts a high-level block diagram of a computer suitable for usein performing the functions described herein. As depicted in FIG. 4, thesystem 400 comprises one or more hardware processor elements 402 (e.g.,a central processing unit (CPU), a microprocessor, or a multi-coreprocessor), a memory 404, e.g., random access memory (RAM) and/or readonly memory (ROM), a module 405 for resolving domain name systemqueries, and various input/output devices 406 (e.g., storage devices,including but not limited to, a tape drive, a floppy drive, a hard diskdrive or a compact disk drive, a receiver, a transmitter, a speaker, adisplay, a speech synthesizer, an output port, an input port and a userinput device (such as a keyboard, a keypad, a mouse, a microphone andthe like)). Although only one processor element is shown, it should benoted that the computer may employ a plurality of processor elements.Furthermore, although only one computer is shown in the figure, if themethod 300 as discussed above is implemented in a distributed orparallel manner for a particular illustrative example, i.e., the stepsof the above method 300, or the entire method 300 is implemented acrossmultiple or parallel computers, then the computer of this figure isintended to represent each of those multiple computers.

Furthermore, one or more hardware processors can be utilized insupporting a virtualized or shared computing environment. Thevirtualized computing environment may support one or more virtualmachines representing computers, servers, or other computing devices. Insuch virtualized virtual machines, hardware components such as hardwareprocessors and computer-readable storage devices may be virtualized orlogically represented.

It should be noted that the present disclosure can be implemented insoftware and/or in a combination of software and hardware, e.g., usingapplication specific integrated circuits (ASIC), a programmable gatearray (PGA) including a Field PGA, or a state machine deployed on ahardware device, a computer or any other hardware equivalents, e.g.,computer readable instructions pertaining to the method(s) discussedabove can be used to configure a hardware processor to perform thesteps, functions and/or operations of the above disclosed method. In oneembodiment, instructions and data for the present module or process 405for resolving domain name system queries (e.g., a software programcomprising computer-executable instructions) can be loaded into memory404 and executed by hardware processor element 402 to implement thesteps, functions or operations as discussed above in connection with theillustrative method 300. Furthermore, when a hardware processor executesinstructions to perform “operations,” this could include the hardwareprocessor performing the operations directly and/or facilitating,directing, or cooperating with another hardware device or component(e.g., a co-processor and the like) to perform the operations.

The processor executing the computer readable or software instructionsrelating to the above described method can be perceived as a programmedprocessor or a specialized processor. As such, the present module 405for resolving domain name system queries (including associated datastructures) of the present disclosure can be stored on a tangible orphysical (broadly non-transitory) computer-readable storage device ormedium, e.g., volatile memory, non-volatile memory, ROM memory, RAMmemory, magnetic or optical drive, device or diskette and the like.Furthermore, a “tangible” computer-readable storage device or mediumcomprises a physical device, a hardware device, or a device that isdiscernible by the touch. More specifically, the computer-readablestorage device may comprise any physical devices that provide theability to store information such as data and/or instructions to beaccessed by a processor or a computing device such as a computer or anapplication server.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and nota limitation. Thus, the breadth and scope of a preferred embodimentshould not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A method comprising: receiving, via a processor,a domain name system query that specifies a domain name of a destinationresiding in a private network space; routing, via the processor, thedomain name system query to a top-level domain name system serverassociated with the private network space, without routing the domainname system query to a server in a public Internet space, wherein thetop-level domain name system server resides in a highest level of ahierarchy of domain name system servers belonging to the private networkspace; receiving, via the processor, a response from the top-leveldomain name system server, wherein the response identifies an internetprotocol address associated with a second domain name system server thatresides in a lower level of the hierarchy relative to the top-leveldomain name system server; and routing, via the processor, the domainname system query to the second domain name system server, using theinternet protocol address specified in the response from the top-leveldomain name system server.
 2. The method of claim 1, further comprising:receiving a response from the second domain name system server, whereinthe response includes an internet protocol address associated with athird domain name system server that resides in a lower level of thehierarchy relative to the second domain name system server; and routingthe domain name system query to the third domain name system server,using the internet protocol address specified in the response from thesecond domain name system server.
 3. The method of claim 1, furthercomprising: receiving a response from the second domain name systemserver, wherein the response includes an internet protocol addresscorresponding to the domain name of the destination; and routing theresponse from the second domain name system server to a source of thedomain name system query.
 4. The method of claim 3, wherein the responsefrom the second domain name system server is routed to the source via aload balancer.
 5. The method of claim 3, wherein the response from thesecond domain name system server is routed to the source via a mobilitydomain name system server associated with a mobility subdomain.
 6. Themethod of claim 1, wherein the private network space is part of aninternet protocol multimedia subsystem network.
 7. The method of claim6, wherein the destination is an interrogating call session controlfunction element of the internet protocol multimedia subsystem network.8. The method of claim 6, wherein the destination is a serving callsession control function element of the internet protocol multimediasubsystem network.
 9. The method of claim 6, wherein the private networkspace is a private multiprotocol label switching space.
 10. The methodof claim 1, wherein the destination is part of a subdomain that providesa voice over long term evolution service.
 11. The method of claim 1,wherein the destination is part of a subdomain that provides a carriervoice over internet protocol service.
 12. The method of claim 1, whereinthe destination is part of a subdomain that provides an internet imagingprotocol service.
 13. The method of claim 1, wherein the destination ispart of a subdomain that provides a web real-time communication service.14. A non-transitory computer-readable storage device storing aplurality of instructions which, when executed by a processor, cause theprocessor to perform operations, the operations comprising: receiving adomain name system query that specifies a domain name of a destinationresiding in a private network space; routing the domain name servicequery to a top-level domain name service server associated with theprivate network space, without routing the domain name system query to aserver in a public Internet space; receiving a response from thetop-level domain name system server, wherein the response identifies aninternet protocol address associated with a second domain name systemserver that resides in a lower level of a hierarchy relative to thetop-level domain name system server; and routing the domain name systemquery to the second domain name system server, using the internetprotocol address specified in the response from the top-level domainname system server.
 15. The non-transitory computer-readable storagedevice of claim 14, wherein the operations further comprise: receiving aresponse from the second domain name system server, wherein the responseincludes an internet protocol address associated with a third domainname system server that resides in a lower level of the hierarchyrelative to the second domain name system server; and routing the domainname system query to the third domain name system server, using theinternet protocol address specified in the response from the seconddomain name system server.
 16. The non-transitory computer-readablestorage device of claim 14, wherein the operations further comprise:receiving a response from the second domain name system server, whereinthe response includes an internet protocol address corresponding to thedomain name of the destination; and routing the response from the seconddomain name system server to a source of the domain name system query.17. The non-transitory computer-readable storage device of claim 16,wherein the response from the second domain name system server is routedto the source via a load balancer.
 18. The non-transitorycomputer-readable storage device of claim 14, wherein the destination ispart of a subdomain that provides a voice over long term evolutionservice.
 19. The non-transitory computer-readable storage device ofclaim 14, wherein the destination is part of a subdomain that provides acarrier voice over internet protocol service.
 20. An apparatuscomprising: a processor; and a computer-readable storage device storinga plurality of instructions which, when executed by the processor, causethe processor to perform operations, the operations comprising:receiving a domain name system query that specifies a domain name of adestination residing in a private network space; routing the domain nameservice query to a top-level domain name service server associated withthe private network space, without routing the domain name system queryto a server in a public Internet space; receiving a response from thetop-level domain name system server, wherein the response identifies aninternet protocol address associated with a second domain name systemserver that resides in a lower level of a hierarchy relative to thetop-level domain name system server; and routing the domain name systemquery to the second domain name system server, using the internetprotocol address specified in the response from the top-level domainname system server.